When using a microwave oven to prepare a hot beverage, the microwave energy causes the water molecules to oscillate and generate heat. In many cases, the objective of heating in a microwave oven is to heat the liquid to the boiling point. The precise amount of time required to boil the liquid is often uncertain, and as a result it is common to heat the liquid for a longer period than is necessary.
On occasion people sometimes forget the liquid has been heated in the microwave, causing them to need to reheat the liquid because it has cooled. The process of reheating the liquid results in removing dissolved oxygen and makes it possible to heat the water above the boiling point, sometimes called “superheating.”
Many cups or other containers used to boil water are also quite smooth on their inner surfaces, and the smooth surfaces tend not to be conducive to boiling because they do not contain nucleation sites to facilitate boiling. The combination of imprecise heating, occasional reheating, and containers without nucleation sites makes superheating even more likely.
There have been prior efforts to produce devices that aid in preventing superheating. For example, U.S. Pat. No. 7,038,181 to Edmark describes a lid for placement atop any cup or container, in which the lid includes a stem that extends into the container. The stem is formed from a material having nucleation sites, and therefore it facilitates boiling. The separate lid, however, is imprecise and does not fit all vessels. It also is primarily designed for a single cup or mug, rather than a true kettle for a larger volume. The arrangement of the lid can also be awkward or difficult to use in order to avoid being burned by hot steam escaping from the mug.